Power devices are utilized in a plurality of circuit applications that require high voltage and current capability, for example, automotive circuits. However, even power devices must be protected from large surge currents which could destroy the device.
Control circuits are typically utilized to protect power transistors by, for example, monitoring the current flowing through the power transistor. One type of control circuit for protecting a power device is fully disclosed in U.S. Pat. No. 5,285,346 issued to Davies et al. on Feb. 8, 1994 and entitled "CURRENT DRIVEN CONTROL CIRCUIT FOR A POWER DEVICE". However, the control circuit disclosed here is a current driven control circuit wherein a current driven control circuit requires its input to be clamped.
There also exists control circuits that are voltage driven. However, such control circuits are typically implemented such that they monitor conditions of a power transistor after power has already been supplied to the power transistor. Thus, this has the disadvantage of damaging the power transistor in the case of quick and large surge signals wherein the control circuitry can not act in a sufficient amount of time to prevent damage to the power transistor.
Hence, there is a need for an improved voltage driven circuit for protecting a power device that monitors the input signal to the power transistor before the signal is applied to the transistor.